# Forces: Gravity, Friction, Constant

19. An 80N crate slides with constant speed a distance of 5.0m downward along a rough slope that makes an angle of 30 degrees with the horizontal. The work done by the force of gravity is:

A. -400J

B. -200J

C. -69J

D. 200J

E. 400J

20. A man pulls a sled along a rough horizontal surface by applying a constant force F at an angle theta above the horizontal. In pulling the sled a horizontal distance d, the work done by the man is:

A. Fd

B. Fdcos(theta)

C. Fdsin(theta)

D. Fd/cos(theta)

E. Fd/sin(theta)

21. A man wishes to pull a crate 15 m across a rough floor by exerting a force of 100M. The coefficient of kinetic friction is 0.25. For the man to do the least work, the angle between the force and the horizontal should be:

A. 0

B. 14 degrees

C. 43 degrees

D. 66 degrees

E. 76 degrees

22. A particle moves 5m in the positive x direction while being acted upon by a constant force F = (4N)i + (2N)j - (4N)k. The work done on the particle by this force is:

A. 20 J

B. 10 J

C. -20J

D. 30J

E. is impossible to calculate without knowing other forces

23. A block is attached to the end of an ideal spring and moved from coordinate xi to coordinate xf. The relaxed position is at x = 0. The work done by spring is positive if:

A. xi = 2cm and xf = 4cm

B. xi = -2cm and xf = 4cm

C. xi = -2cm and xf = -4cm

D. xi = 2cm and xf = -4cm

E. xi = -4cm and xf = -2cm

https://brainmass.com/physics/work/forces-gravity-friction-constant-72887

#### Solution Summary

This solution involves calculations for various questions involves forces that include gravity, friction, and a constant force.